Re: [PATCH 1/2] ads7846: Make buffers in ads7846_read12_ser and ads7845_read12_ser DMA save

[Alexander Stein <alexander.stein@systec-electronic.com>]

Hello,

Am Mittwoch, 4. Mai 2011, 17:49:56 schrieb Jonathan Cameron:
> On 05/04/11 16:22, Alexander Stein wrote:
> > req.sample needs its own cacheline otherwise accessing req.msg fetches
> > it in again.
> > Put req onto stack as it doesn't need to be DMA save.
> > req.sample is kzalloced itself for DMA access.
> > req.command doesn't need own cache line because it will only be written
> > to memory on dma_map_single. req.scratch is unsed at all.
> > 
> > Note: This effect doesn't occur if the underlying SPI driver doesn't use
> > DMA at all.
> 
> How about using ____cacheline_aligned having moved 'sample' to the end of
> the structure?
> 
> e.g.
> 
> ...
> struct spi_transfer xfer[6];
> __be16  sample ____cacheline_aligned;
> }
> 
> Rather smaller patch when you get down to it.

Mh, I didn't know I had to reorder the struct elements to use 
____cacheline_aligned. I originally had a solution in mind with a smaller 
memory footprint in mind, but rethinking about it, this might be negligible if 
there is one at all.
So, if ____cacheline_aligned is the more sane approach I'll resend a patch 
using it.

Alexander